Gripper conveyors of the aforesaid kind are known to the art and are often used to pick-up, in a given position, newspapers or like flat articles which are conveyed in mutually overlapping relationship on a conveyor path and for releasing transported newspapers and like flat articles at another position along the chain. It should be mentioned here that the term "newspaper" as used in this document is meant to include any type of printed matter and like flat articles.
The grippers are opened and the gripper conveyor is controlled in a manner such that the free edge of the movable clamping jaws will engage in the overlapping stream, wherewith the next following newspaper in the stream will move into the open gripper due to a difference in speed between the newspaper stream and the gripper conveyor.
In order to limit the complexity of the gripper conveyor and to ensure that the grippers will function effectively, particularly with regard to manufacturing costs, it has been suggested to use grippers of the aforedescribed, i.e. grippers which are permanently spring-biased towards a closed position.
The grippers are opened by activating the movable clamping jaw with the aid of the maneuvering arm, by causing the manouvering arm to run on a guide bar or rail such as to swing the manouvering arm, wherein the length of the bar determines the time period over which the gripper is held open. When the gripper opens, the free edge of the movable clamping jaw is swung down to a given level determined by the level of said guide bar. In the open position of the gripper, the level on which the free edge of the movable clamping jaw is located will correspond to the level of the exposed upper surface of a newspaper in the overlapping newspaper stream on the conveyor path. This causes problems related to the varying levels of the upper surfaces of respective newspapers, for instance as a result of varying thickness of the newspapers or like publications, the varying extent to which the newspapers overlap, and so on. This problem is accentuated when the conveyor is stopped and also at the end of a stream of mutually overlapping newspapers.
Publication EP 0 356 521 teaches a conveyor which includes grippers which are highly complex, insofar as the movable clamping jaw/clamping jaws of the gripper include a pivot journal and a latching mechanism between their driving end and their clamping end. The latching mechanism is brought to a clamping jaw latching state and a clamping jaw releasing state by means other than the means used to open the gripper against the action of a spring force. Furthermore, this known gripper is not permanently biased towards a closed gripper position, and the movable clamping jaw moves rectilinearly against the action of the spring means.